In a mobile communication system including a base station (BS) that provides a wireless communication service and a mobile station (MS), the MS is generally located in an area (service area of the BS) in which the BS can provide the service. When an MS is in a service area of a BS, the MS can communicate with a server or the like on a network via the BS. However, even when the MS is located in the service area, if the MS moves in the shade of a building or the like, the MS may not be able to receive radio waves from the BS and may temporarily be in a state (out-of-service) in which the MS cannot communicate. If the MS becomes out-of-service, an application performing communication between the BS and the MS is disconnected, or interrupted. Thereafter, the application can restart the communication when the MS receive radio waves from the BS.
However, in a case of an application that transmits file data by using FTP (File Transfer Protocol), if the connection is disconnected during communication, the file data has to be transmitted/received again from the beginning. As a result, resources such as time and frequency band are wasted. Therefore, even if the MS becomes a state of out-of-service, there is a request to maintain the connection of the application as much as possible. In a case of file transmission using FTP, if the connection is disconnected while transmitting file data, basically, the file is transmitted again from the beginning.
Here, as a method for maintaining the connection of application even in a state of out-of-service, there is a method that uses a dormant mode. When no data has been transmitted for a time period, the connection comes to the dormant mode (dormant state) that disconnects only a connection in a lower layer while maintaining a connection in an upper layer. For example, the upper layer is a session layer, and the lower layer is a link layer. When restarting communication, the dormant mode restarts communication by restoring (reconnecting) the connection in the lower layer.
Originally, the object of the dormant mode is to efficiently use resources in a service area. By applying the dormant mode when out-of-service is detected, the connection of the application can be maintained even in a state of out-of-service. When the connection in the lower layer is restored, the application can restart communication from a state before the MS entered an out-of-service area.
On the other hand, there is a technique in which a wireless communication mobile station refers to data that have been transmitted/received for a predetermined period in the past and determines a cycle for searching a base station on the basis of the reference result, the mobile station determining that the mobile station is in an out-of-service area of a base station.
Japanese Unexamined Patent Application Publication No. 2008-160303 is an example of related art.
MITF Dial-up Dormant Protocol Specifications (ARIB STD-T78 ver. 1.0) Jul. 27, 2001, Association of Radio Industries and Businesses is an example of related art.